Conventionally, an ink-jet recording apparatus used as an image recording apparatus (image forming apparatus) such as a printer, a facsimile, a copier or the like can form an image on a sheet of paper (not necessarily limited to paper but whatever is used to form an image thereon) by ejecting ink droplets from a nozzle of an ink-jet head thereto. Since deviation of the positional relationship between the sheet of paper and the ink-jet head may degrade image quality, it is required to convey the sheet of paper with accuracy.
Since the ink-jet recording apparatus allows ink droplets to adhere on a sheet of paper, the paper tends to become corrugated. Namely, within a few seconds after the ink droplets adhere on the paper, the paper swells and then becomes corrugated, which is known as so-called cockling. Typically, when an image is printed on a sheet of paper, there are margins formed on the right, left, top, and bottom of the paper. Therefore, tensile stress is caused between the right (left) margin and a printed area adjacent to the right (left) margin, which pulls both the margins inward, thereby causing both side portions of the paper to rise. If this happens, the paper cannot be flat in relation to the ink-jet head, and a gap between the paper and the ink-jet head varies, thereby distorting the image. Moreover, a large corrugation of the paper causes a problem in that the image printed on the paper may be defective and the ink-jet head may be damaged or broken since the paper can contact the ink-jet head.
In order to eliminate such disadvantages, an image forming apparatus such as an ink-jet printer has been proposed in recent years, where a conveyor roller is disposed in both the upstream and the downstream end of a paper conveying direction so as to maintain the flatness of the paper in relation to the ink-jet head. Such an image forming apparatus can prevent the paper from becoming corrugated during printing (See, patent-related publications listed below).
[Patent-related document 1] Japanese Patent Application Laid-Open Publication No. H7-125364.
[Patent-related document 2] Japanese Patent Application Laid-Open Publication No. H7-132659.
[Patent-related document 3] Japanese Patent Application Laid-Open Publication No. H9-24650.
[Patent-related document 4] Japanese Patent Application Laid-Open Publication No. 2001-261188.
However, in such an ink jet recording apparatus where the conveyor rollers are provided in the upstream and the downstream end of the paper along the conveying direction, an image is printed on the paper while the conveyer rollers are holding the leading and the rear ends of the paper. Therefore, a relatively larger non-printed zone has to be allocated at the upper and lower portions of the paper (i.e., the leading margin and the rear margin), which leads to another problem in that the printable area becomes smaller.
The present invention has been made in view of the above, and may provide a paper conveying apparatus, an image forming apparatus and an ink-jet recording apparatus that can press side portions of paper downward so as to allow the paper to bend downward.